1. Field of the Invention
The present invention relates to an image-forming apparatus, and more specifically to an image-forming apparatus such as an electrophotographic apparatus using a dry double-component developer.
2. Description of the Related Art
Conventionally, for an image-forming apparatus, a development process using a double-component developer which comprises magnetic carriers and toners has been employed, in which a magnetic brush is formed of the double-component developer. An image-forming apparatus that employs the development process with a double-component developer contains a rotatably supported cylindrical development sleeve as a developer carrier, which comprises a magnetic roller having a magnet body with a plurality of pairs of magnetic poles. In the image-forming apparatus, the cylindrical development sleeve further has toners adhered to carriers on its surface, and the toners are transferred to a development area, in which developing is carried out.
A development process using a one-component developer has also been employed, in which the one-component developer consists of either magnetic toners or non-magnetic toners. In the development process using a one-component developer, an image-forming apparatus has different structures and means for charging toners from the development process with a double-component developer. In both of the processes, however, developing is carried out by having toners on a surface of a development sleeve, and then by transferring the toners to a development area.
Japanese Patent Application Publication (JP-B) No. 64-12386 discloses a method of improving a quality of an image by roughening a surface of a development sleeve so as to transfer toners in an improved state. As described in Japanese Patent Application Laid-Open (JP-A) No. 05-19632, a surface of a development sleeve is roughened so as to transfer toners in an improved state, in a development process using a double-component developer.
In the aforementioned methods, developing is carried out by a non-contacting developing method. The non-contacting developing method is a method to determine a certain amount of a developer to be transferred onto a developer bearing member, by using a developer limiting member. A contacting (impression) developing method requires a developer limiting member made of rigid or rigid and magnetic materials. The contacting developing method therefore has a difficulty in supplying a sufficient amount of developer onto a developer bearing member. Carriers are also required to have a smaller particle diameter, in accordance with an increasing demand for a high-quality and miniaturized apparatus. The smaller diameter a carrier has, the poorer the fluid ability of the carrier is. A developer having carriers with a smaller diameter hence has a difficulty in stably transferring into a development area.
For the purpose of economizing and reducing the cost of maintenance services, image-forming devices such as a copier is usually constructed in one-piece structure in which a photoconductor (latent electrostatic image support) and a developing device are attached. The image-forming device allows a service person to easily replace the photoconductor and the developing device. In this case, a photoconductor and a developing device should be replaced at a long interval, otherwise the cost increases. A developer having a long lifetime, and a photoconductor having almost the same lifetime as the photoconductor are necessary. In the contacting developing method employing a double-component developer, a photoconductor is abraded by the developer. The developer is unlikely to have a longer lifetime, accordingly. A demand has also been made on widening a density for supplying a developer in order to obtain a higher quality of image. The higher the density for supplying a developer is, the more a photoconductor is abraded. Filler is added to a protecting layer of a photoconductor, so as to prevent abrasion on the photoconductor. Abrasion is certainly prevented, however, resolution deteriorates, and a blurred image is more likely to be produced, because of substances such as ozone, nitrogen oxide, a nitric acid ionic substance, ammonium ionic substances, and the like, all of which are cumulated on a surface of the photoconductor, and induce a blurred image.